I'm turning my blog into a Dear Tango-Abby for just a moment. This kind of question has turned up on other blogs and forums, so I thought I'd address it more thoroughly here. The usual caveat applies - what follows is my opinion from my observations, and may or may not be relevant in other tango communities. YMMV.
From my email . . .
"There's a leader that I really like, but he's never asked me to dance. Is it okay to ask him why?"
Short answer: No.
Much longer answer: There might be an opportunity to approach him in a constructive way during practica or a class that you both attend, to simply ask if you might practice sometime on whatever it is you or he is working in class/practica. And then leave it to him. You said in another part of the email that you've tried the casual small talk at the snack table and cabeceo'ing him - so beyond that, depending on the preferences in your community, I would leave it at that.
If, however, it's quite common for ladies to ask gentlemen to dance (and it's a successful practice) then you can give it a try. But don't simply ask him why he hasn't asked you - stay in the present. And if he does turn you down when you ask, then politely say, "all right then, maybe another time" smile and walk away. Don't ask him why, just smile politely and move on. You can, if you know some of the followers he does ask to dance, talk to them casually about how he likes to dance and that sort of thing. That kind of conversation can give you some insight. But just think if the situation were reversed how you might feel if someone approached you that way. Depending on who it was and the situation - it could be very uncomfortable for both of you. The codigos serve to avoid hurt feelings and embarrassment of just this kind.
It's hard not knowing why someone seems to avoid dancing with you. There are leaders in my community that have never asked me to dance, or almost worse, have danced with me once months ago and never asked again. I've cabeceo'd and made small talk, but no dice. Granted, for several months when I started I stumbled and apologized through every tanda. So my first thought is they think I'm a bad dancer. Or I said something wrong - I've done that often enough. Or they don't like something I do, or the way I dress, or... whatever. A girl can make herself crazy wondering about it. The truth is it may have nothing to do with something we've done or how we're dancing. It's hard but try not to spend so much time wondering what's wrong - and focus on the leaders that do want to dance with you. We're there for them - for the leaders who are asking.
My lesson learned...
One night an out-of-town dancer I admire, who comes to Austin very rarely, turned up at the milonga I was attending. We had danced once or twice - but of course I was very green at the time. Clumsy, apologetic, nervous. Twice I tried the cabeceo and twice he looked at me, and then turned away. 'Nuff said. Or rather, not said. It stung. A lot.
While I was nursing my hurt pride, I failed to notice that there were gentlemen present who did want to dance with me and I wasn't meeting their eyes. I was too busy second guessing myself. I lost almost an hour of the milonga licking my wounds. And while I was sitting there not dancing, leaders I love to dance with were wondering why I wasn't meeting their cabeceo.
Stay in the moment. Give your attention, effort and energy to the leaders who do want to dance with you. That's what we're there for.
That's my two cents...